The idea of focusing on the door seals resonates with me.
As I stated initially, I'm trying to get the interior back to the way I remember it: quieter than it is now. Adding Dynamat would undoubtedly do the trick (man, is that stuff expensive!!!); however, if I'm right about the gradual increase in cabin noise over the years, then it just makes sense that some OEM noise dampening material is failing. The door seals seem the logical place to start.
Most significant, in my case, is that a year and a half ago, a deer had the audacity/stupidity
to leap the guard rail on the Taconic Parkway in front of my 126. It's hind quarters swung into my driver's side door causing quite a dent. (And if my 420SEL looked bad, you can imagine what shape the deer was in
I have a great bodyshop up here that did an incredible job restoring the door; however, the comments you've all made lead me to believe that the doorseal may not be properly seated anymore.
Thanks for giving me something to tackle: Seems like an easy enough DIY job. I'll report back with the results.